Bearings find application in many mechanical structures with moving parts, particularly rotating parts. Bearings are provided as e.g. ball-bearings between two relatively rotating parts such as gear components or rotating shafts. By way of example, aircraft have many rotating parts such as generators, motors or actuators. It is important that any failure in such parts can be quickly and reliably identified and that in the event of failure of, e.g., a bearing, the component can continue to operate safely until the failed part can be repaired or replaced.
It is known to provide redundancy in many machine or mechanical systems for parts that might fail, particularly where safety is a primary consideration, such as in aircraft. Secondary or back-up bearings are taught in e.g. U.S. Pat. No. 3,183,043, U.S. Pat. No. 5,993,069 and U.S. Pat. No. 7,299,703 where a secondary bearing or journal bearing, which is normally unloaded—i.e. out of engagement with the rotating part—comes into play in the event that the primary bearing, which is normally loaded—i.e. in bearing engagement with the rotating part—fails. These systems can also provide an indication that the primary bearing has failed and the secondary bearing is in use, so that the primary bearing can be replaced or repaired as soon as possible, thus minimising the time the system has to rely on the emergency, secondary bearing.
In systems where downtime is undesirable and costly, there is a need for a fail safe bearing system where failure of a primary bearing can be easily and quickly identified without the need for complex sensors and the like—such sensors add to the cost, weight and power consumption of a machine or the like, all of which are generally undesirable, especially in e.g. aircraft.
Particularly, but not exclusively, steps are being taken to provide several points of redundancy in aircraft parts to provide tolerance to failure of mechanical components and improve safety as well as reduce down-time. One area where failure can occur is in the bearings provided around rotating shafts.
It is an aim of the present disclosure to provide a fail safe bearing which enables identification of failure of a primary bearing by simple visual and/or tactile inspection.